A tracked vehicle, especially military vehicles such as tanks, generally comprises on each side of the vehicle, a respective track structure comprising an endless track chain, various rollers, sprockets or wheels over which the chain is guided.
The lower pass of the tread chain is held against the ground by at least two running-wheel assemblies and at each end of the lower pass, the chain extends upwardly at an obtuse angle to the lower pass and then around other rollers to form the upper pass of the tread chain.
Generally the chain comprises a multiplicity of tread bars provided with the ground-engaging treads which lie on the outside of the continuous tread chain, and intermediate links which are hingedly connected to each of these bars join them to the next bar of the chain.
Between the tread bars or links, therefore, a gap is formed.
The running-wheel assemblies can comprise a wheel at each end of the lower pass about which the chain runs and which is mounted on a support arm connected to the chassis, usually pivotally, and transmitting force to the chassis via a spring and shock-absorber suspension. In some assemblies, the running wheels or rollers are provided in pairs to either side of a fulcrum arm. Thus each pair of wheels of a given roller assembly includes one wheel or roller about which the chain passes at a respective end of the lower stretch, and another wheel inwardly of the first-mentioned wheel which rests upon the lower tread.
The surfaces which engage these wheels are formed by the tread bars or links and hence the running surface of the chain on the wheels is interrupted since a gap is provided between each tread bar and the next. The connecting links may be disposed outwardly of the lateral surfaces of the wheels so that they are never engaged thereby.
A typical system for bogie and track assemblies for track-laying vehicles of the above-described type can be found at pages 399 to 401, in the publication entitled, Principles of Automotive Vehicles, U.S. Government Printing Office, Washington, D.C. January 1956. Reference is also made to German Pat. Nos. 761,988 and 659,477.
Since the road wheels or running wheels of the track assembly have, at best, line contact on the running surface of the chain links, between these links the wheels tend to drop as the links pass around the wheels. This tends to impart a vertical displacement to the wheel axis and is translated into vertical oscillation of high-energy content of a frequency which is a function of the track speed and the space between the tread links.
While these vertical oscillations are generally taken up by the shock absorber and damper systems of the suspension, a severe stress is placed upon the latter when the track-laying vehicle travels over irregular terrain and even when the vehicle negotiates perfectly level surfaces.
The wear and tear on the suspension is thus pronounced, maintenance costs are high and frequently a vehicle may have to be taken out of service for such maintenance at an inopportune moment. It is, therefore, important to avoid the generation of these vertical oscillations which have been considered inherent in the nature of rigid-link track chains and running-wheel assemblies.